1. Field of the Invention
The present disclosure generally relates to imaging and, more particularly, to an image capture apparatus having an autofocus function.
2. Description of the Related Art
Conventionally, as a general method used for autofocusing (hereinafter, AF) of the image capture apparatus, there are known a phase difference detection method and a contrast detection method. In the phase difference detection method, a light flux that has passed through an exit pupil of a photographic lens is divided into two, the two divided light fluxes are respectively received by a set of focus detection sensors, and a deviation amount between signals output according to the received light amounts, namely, a deviation amount between relative positions of the light fluxes in the dividing direction, is detected to directly acquire a deviation amount in a focus direction of the photographic lens.
Thus, once a storage operation is carried out by the focus detection sensors, an out-of-focus amount and a direction are acquired, thereby enabling a high-speed focus adjustment operation. However, to divide the light flux that has passed through the exit pupil of the photographic lens and acquire the signals corresponding to the respective light fluxes, two sets of a focus detection optical system and a sensor are generally provided, and a detected deviation amount between the signals needs to be converted into an out-of-focus amount.
Unlike the above-described phase difference detection method, in the other method, namely, the contrast detection method, an image sensor is used as a focus detection sensor. This is a method that focuses attention on an output signal of the image sensor, especially a high-frequency component signal, and sets the position of the photographic lens, where a contrast evaluation value indicating the contrast of an object image is largest, as an in-focus position.
The contrast detection method is, however, also referred to as a hill-climbing method. The contrast evaluation value needs to be acquired while driving the photographic lens, and the position where the contrast evaluation value is largest needs to be searched for. Thus, this method is not suitable for a high-speed focus adjustment operation. On the other hand, the method has the advantage of high focusing accuracy because the contrast is evaluated by using the signal acquired from the image sensor.
Recently, Japanese Patent Application Laid-Open No. 2003-156677 has discussed a phase difference detection method using an image sensor that is realized by including a focus detection unit therein.
In the technique discussed in Japanese Patent Application Laid-Open No. 2003-156677, each pixel of the image sensor includes two photoelectric conversion areas, a solid-state image sensor having an output system capable of obtaining signals from a plurality of photoelectric conversion areas and outputting signals separately for each photoelectric conversion area, and a calculation unit that calculates a phase difference and a contrast evaluation value of an object image from the signal output from each of the plurality of photoelectric conversion areas. A focus lens is driven based on the phase difference to perform focusing control, and then the focus lens is driven based on the contrast evaluation value to perform focusing control.
In the technique discussed in Japanese Patent Application Laid-Open No. 2003-156677, the focusing control is easily performed when the number of distance measurement areas is one. However, in the image plane phase difference detection method, if there is a plurality of distance measurement areas, to detect a defocus amount indicating an out-of-focus amount of an imaging optical system, signals output from the two photoelectric conversion areas of each pixel of the plurality of distance measurement areas need to be separately read, and simultaneously subjected to calculation processing. Consequently, there is a possibility that a calculation load and a circuit size will increase. Thus, to detect a phase difference on the image plane in the case of the plurality of distance measurement areas, the distance measurement areas need to be subjected to calculation processing one by one, taking time until an in-focus state is set.